| In recent decades, with the need of city basic construction and the construction technology development of underground project, most of tunnels and underground engineering are constructed completely or partially in weak soil surrounding rock. Xiamen subsea tunnel is the first subsea tunnel to be planned and constructed in our country. Almost thirty percent of its length is located in soil surrounding rock formed by the Quaternary sedimentation or weathering, so it is important to ensure the soil surrounding rock stability of land segment in excavation for itself construction and the display of our construction technology. Now the stability indexes and evaluation methods of soil surrounding rock are the same with the rocky surrounding rock methods in domestic, which don't reflect the characteristics of soil surrounding rock. In addition, the experience is the major way to estimate soil surrounding rock stability and select the pre-reinforcement measure and parameters. Thereby, it is in an urgent need to propose an explicit and user- friendly the stability indexes and evaluation methods, which can comprehensively show the stability of soil surrounding rock, and the excavation method and pre-reinforcement measure. Aiming at the solution of major problems of soil surrounding rock in Xiamen subsea tunnel, this thesis makes a systemic research on rock mass classification of sandy tunnel and arrives at conclusions as follows:1. The physical and mechanical parameters of each geological subsection in land segment of Xiamen subsea tunnel, divided by testing and investigation , are obtained, and the disintegration of soil surrounding rock in land segment is tested. The deformation and failure of surrounding rock which are analyzed according to monitoring data are used for verifying the validity of geological subsection. The problems in the design and construction are also analyzed.2. Aiming at clayey surrounding rock and sandy surrounding rock in this tunnel, a new evaluation index system of stability is established by geotechnical test, investigation materials and theory analysis. The values of stability index are grouped, and the basic steady excavated span of each group is studied through model test, numerical simulation. The sub-classification method of soil surrounding rock is established according to the basic steady excavated span, and then the sub-classification of soil surrounding rock in land segment is divided.3. Based on the results of investigation materials and model test, the failure mode of soil surrounding rock is summarized and defined, and the influence factors of surrounding rock failure is discussed. The mechanism of failure modes is analyzed by critical measure, including occurring, transforming and unifying. The possible failure mode of all levels of soil surrounding rock in land segment of Xiamen subsea tunnel, using theory failure condition which is developed according to the failure mechanism, can be obtained.4. Depending on the influence on stability of soil surrounding rock from construction span, excavated length, closing time and distance of primary support and the length of bench, and combining with the research of self-stability span, this paper proposes the determination principle of construction method and parameters and pre-reinforcement level, which is applied in double lane and three lane soil tunnel and in land segment of Xiamen subsea tunnel to determine construction method and parameters.5. According to the pre-reinforcement mechanism of small pipe, grouting and frontal blot, the adaptability of their single or combination reinforcement measures and surrounding rock type and failure mode are analyzed. Their pre-reinforcement effect is contrasted through the results of model test on the base of adaptability analysis. The select principle of pre-reinforcement measures, developed based on the analysis of adaptability and reinforcement effect, is used for determining pre-reinforcement measures of soil surrounding rock in land segment of Xiamen subsea tunnel. Utilizing double-parameter model of foundation, the deflection and internal force of small pipe were deduced, and tunnel face stability is also analyzed after pre-reinforcing. Taking the deflection, internal force of small pipe meeting the design requirements that is optimum, and stability of tunnel face after pre-reinforcing as a principle, the design method of small pipe pre-reinforcing parameters is generated. Pre-reinforcing parameters of small pipe of each sub-grade of soil surrounding rock in land segment of Xiamen subsea tunnel are ascertained.
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